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Percona Blog0 Hot0 comments6 min read
The diagnostic data MongoDB Atlas doesn’t hand you
MongoDB's Full Time Diagnostic Data Capture (FTDC) records ~5,700 metrics per second into a diagnostic.data folder — the first thing MongoDB support requests during performance incidents. On self-managed servers this file is directly accessible, but on Atlas it's hidden: not in the UI, not in the log download, and undocumented. There is an undocumented API endpoint that packages FTDC on demand using three API calls, requiring a programmatic API key and the internal replica set name (not the display name). A critical gotcha: Atlas sets the FTDC directory size limit to 400 MB (double the default), which on a busy production cluster retains only 2–5 days of history before oldest files are silently deleted. The key operational advice is to pull FTDC data during an incident, not after — by the time a postmortem is scheduled, the data may be gone. Two tools for reading FTDC are mentioned: keyhole (Grafana-based dashboards) and Big Hole (browser-only, no upload required, supports Atlas tarballs directly).
Source: https://www.percona.com/blog/the-diagnostic-data-mongodb-atlas-doesnt-hand-you. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.
